A Molecular Meanfield Model for the Biaxial Rectangular Discotic Phase with Herring-Bone Packing of Tilted Molecules
01 May 1995-Molecular Crystals and Liquid Crystals (Taylor & Francis Group)-Vol. 264, Iss: 1, pp 165-179
TL;DR: In this article, a molecular mean field model for a rectangular columnar to hexagonal columnar phase transition is presented, assuming the molecules basically to be biaxial objects.
Abstract: A molecular meanfield model for a rectangular columnar to hexagonal columnar phase transition, as observed in case of the HAT series, is presented here assuming the molecules basically to be biaxial objects The theory is developed for a rectangular lattice having herring-bone packing of the tilted molecules Various types of phase diagrams for a homologous series are reproduced for different values of molecular biaxiality Some of them are very similar to the experimentally observed cases but others, particularly involving biaxial nematic phase, are not yet observed It is shown that a gradual lowering of biaxiality with the addition of flexible chain segments can lead to the full phase sequence observed in the HAT series
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TL;DR: In this paper, the structures of columnar mesophases that depend on the presence of either N-H⋯O, or H-O-Bonds (subsumed under the term ‘N|H|O-bonds') are reviewed.
Abstract: The structures of supramolecular columnar mesophases that depend on the presence of either N–H⋯O, or N⋯H–O– hydrogen bonds (subsumed under the term ‘N|H|O-bonds’) are reviewed. The thesis is supported that supramolecular mesogenes bridge different fields of liquid crystal research, offering the opportunity to create a unified picture of thermotropic, and lyotropic mesomorphism. With the examples of N|H|O hydrogen bond mesogenes the molecular structures of the respective mesogenes are presented, and general principles to rationally construct such molecules are discussed. A connection is drawn to systems from isolated columns as found in low molecular weight organogels. Perspectives, and outlooks for possible applications of N|H|O hydrogen bonded columnar phases are given.
116 citations
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TL;DR: The results point to the formation of dynamical structural defects along the columns in stacks of liquid-crystalline tetraalkoxy-substituted, metal-free phthalocyanines.
Abstract: We present a joint molecular dynamics (MD)/kinetic Monte Carlo (KMC) study aimed at the atomistic description of charge transport in stacks of liquid-crystalline tetraalkoxy-substituted, metal-free phthalocyanines. The molecular dynamics simulations reproduce the major structural features of the mesophases, in particular, a phase transition around 340 K between the rectangular and hexagonal phases. Charge transport simulations based on a Monte Carlo algorithm show an increase by 2 orders of magnitude in the hole mobility when accounting for the rotational and translational dynamics. The results point to the formation of dynamical structural defects along the columns.
81 citations
References
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01 Jan 1970
TL;DR: In this paper, the authors present a NMR study of the transition of a mixture of two Isomeric Cyano-Ester homologous series, showing that the phase transition of one of the two isomeric versions of this series is a transition of the other.
Abstract: Some Novel Ferroelectric Smectic Liquid Crystals.- Liquid Crystalline Esters of Phenylhydroquinone and 3-Phenyl 4-Hydroxybenzoic Acid.- The Synthesis and Characterization of Some Perylene and Anthraquinoic Dichroic Dyes for Liquid Crystal Display Applications.- Some New Thermotropic Discogens.- Syntheses and Properties of Liquid Crystalline Heterocycloalkanes.- Characterization of Two Isomeric Cyano-Ester Homologous Series -I.- Effects of Molecular Length on Nematic Mixtures - IV: Structure Effects on Viscosity of Ester Mixtures.- Orientational Disorder in Smectic Liquid Crystals: An Aspect of Structure that has to be Included.- Effect of Molecular Structure of Rigid - Flexible Polyesters on Their Thermotropic Liquid Crystalline Properties.- Relationships Between Molecular Structure and the Incidence of Crystal B and Hexatic B Phases.- Characterization of the Phases of Two Isomeric Cyano-Ester Homologous Series - II.- Unusual Glass Transition of Smectic Liquid Crystal in p-n-Hexyloxybenzylidene-p'-Butylaniline.- Some High Electric Field Effects in Nematic Liquid Crystals.- Application of Generalized Van Der Waals Theory of Homologous Nematogens - Part 1: Trans-4-Ethoxy-4'-N-Alkanoyloxyazobenzenes..- Application of Regular Solution Theory to Discotic Mesophases: Calculation of Phase Diagrams Exhibiting Minima.- Extension of McMillan's Model to Liquid Crystals of Disc-Like Molecules.- Thermotropic Liquid-Crystalline Polymers with Mesogenic Groups and Flexible Spacers in the Main Chain.- Effect of Mesogenic Unit and Spacer Structures on the Thermotropic Properties of Main Chain Liquid Crystal Polyesters.- The Role of Sequence Distribution on Liquid Crystalline Properties of Aromatic Copolyesters.- Diffusion of Rigid Polyamides Through Swollen Gel of Same.- The Molecular Weight Dependence of the Splay and Bend Elastic Constants of a Polymer Liquid Crystal.- DSC, Miscibility and X-ray Studies of the Thermotropic Liquid Crystalline Polyesters with Aromatic Moieties and Flexible Spacers in the Main Chain.- Influence of the Leprosy Drug, Dapsone, on the Phase Transitions of the Lyotropic, Dipalmitoy1 Phosphatidylcholine (DPPC).- Nonaqueous Lyotropic Liquid Crystals of Lecithin and Oligomers of Polyethylene Glycols.- The Diamagnetic Anisotropy of Lyotropic Nematic Mesophases.- Physical Models of Lipid Membranes in Latent Cancer Cells: Ordering Effects of Petroleum Hydrocarbons.- Adiabatic Compression: A New Method to Measure Latent Heats in Phospholipid Bilayers.- Anisotropy of the Electric Conductivity in Amphiphilic Liquid Crystals.- Phase Transition Properties of Bilayers of Mixed Lipids and Their Covalent Analogs.- On The Orientation of Liquid Crystals by Monolayers of Amphiphilic Molecules.- Refractive Index Measurements Using a Double Arm Converging Beam Interferometer.- A Pulsed NMR Study of Transient and Persistent Molecular Order in Nematic Liquid Crystals.- The Effect of Twist on Biaxial Ordering in the Cholesteric Phase.- Deuteron Magnetic Relaxation and Molecular Dynamics in Thermotropic Liquid Crystals.- An Effective Proton Hyperfine Tensor for Di-Tertbutylnitroxide.- Alkyl Chain Flexibility in Liquid Crystals.- Orientational Order in Binary Mixtures of Nematic Liquid Crystals.- The Effect of the Tricritical Region on the Smectic A - Smectic C Transition.- Spatial Correlations in Nematic Liquid Crystals.- Molecular Structure and Ordering in Liquid Crystals.- New Liquid Crystals, Polymeric and Monomeric, Derived From Binaphthyl.- Ioneneomeric Liquid Crystals.- Mesomorphic Properties of an Homologous Series of Alkyl-Terminated Enamine-Ketone Containing Liquid Crystals.- Liquid Crystalline Polymers with Amphiphilic and Non Amphiphilic Side Chains - Effect of the Main Chain on the Phase Behaviour.- The Fluid Mesophases of Polar Rods.- The Nematogeneity of Some Hydrocarbons.- Some Heterocyclic Analogues of Biphenyl Mesogens.- Alignment of Liquid Crystal Molecules on Various Surfaces: Myths, Theories, Facts.- Development of Dual-Frequency Addressable Liquid Crystals.- Dielectric Studies of Monoester and Diester Nematogens.- Intermolecular Guest-Host Interactions and the Optical Order Parameter of Pleochroic Dyes.- Liquid Crystal Alignment on Substrate Surfaces, A Collective Phenomenon.- Alignment of Liquid Crystals in the Vicinity of the SmA-N Transition.- Nematic-Substrate Interaction and the Boundary Layer Phase Transition.- Optical Properties of the Blue Phase of Cholesteric Liquid Crystals.- Lattice Parameters in Blue Phase Mixtures.- Blue Phase Structure Analysis by Optical Bragg Diffractions.- Mesomorphic Polymers as Three Component Systems.- Colloidal Crystals and Glasses.- Self Diffusion Constant and Viscosity of Charged Polystyrene Colloids.- Influence of Molecular Conformation on the Helical Twisting Power of Terpenes in Nematic Liquid Crystals.- Vibrational Spectra of Liquid Crystals XIII: Crystallization Kinetics Study of 4, Octyloxy, 4', Cyano Biphenyl by Rapid Raman Spectroscopy..- Nuclear Spin-Lattice Relaxation Due to Orientational Fluctuation in Smectic Liquid Crystals.- NMR Studies of Molecules Oriented in Mixed Thermotropic Liquid Crystals of Opposite Diamagnetic Anisotropies.- Discotic Mesophase: A Complementary Review.- Identification of the Structure of Mesomorphic Polymers by Means of their Miscibility.- Effect of Molecular Structure on Mesomorphism: Difluorinated Siamese Twin Mesogens.- Anisotropy Induced in a Semi-Flexible Polymer by a Liquid-Crystalline Solvent.- Electrooptical Behaviour of a Novel Strong-Weak Anchored Nematic Layer: First Measurements of MBBA Flexoelectric Coefficient of Splay elz.- On Thermotropic Disc-Like Mesogens.- On The Nature of the Smectic-C Phase.- Contributors.
1,035 citations
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TL;DR: In this article, the Maier-Saupe model with an orientational order parameter is extended to the smectic $A$ phase by introducing a new order parameter, the amplitude of a density wave in the direction of the nematic preferred axis.
Abstract: The Maier-Saupe model of the nematic phase with an orientational order parameter is extended to the smectic $A$ phase by introducing a new order parameter, the amplitude of a density wave in the direction of the nematic preferred axis. Self-consistent equations for the two order parameters are derived from an anisotropic model interaction and are solved numerically. We calculate the order parameters, the entropy, and the specific heat as a function of temperature for several values of dimensionless interaction strength $\ensuremath{\alpha}$ for the smectic $A$ phase. The transition temperatures plotted versus $\ensuremath{\alpha}$ provide a theoretical phase diagram which resembles experimental plots of transition temperature versus alkyl chain length for homologous series of compounds. The model qualitatively reproduces chemical trends in transition entropies. Experiments are suggested to measure the order parameters in the smectic $A$ phase.
854 citations
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TL;DR: In this article, a simple model for an interacting liquid of particles lacking an axis of rotational symmetry is proposed, and the four order parameters necessary to describe an ordered phase are identified.
Abstract: A simple model for an interacting liquid of particles lacking an axis of rotational symmetry is proposed. The four order parameters necessary to describe an ordered phase are identified. An ensemble of such particles is described by a mean field theory. A phase diagram showing both uniaxial and biaxial phases results. The model predicts a phase diagram similar to that of the phenomenological model of Alben.
394 citations